The invention relates to photoflash lamps and particularly to photoflash lamps which are activated electrically.
Such lamps are generally classified into two varieties: low-voltage and high-voltage. Low-voltage photoflash lamps typically include a glass envelope with a combustion-supporting gas (e.g. oxygen) and a quantity of filamentary, combustible material (e.g. shredded zirconium) therein. A pair of electrically conductive lead wires are usually sealed in one end of the envelope and extend therein. A filament is utilized and interconnects the extending ends of the wires. When the filament is heated by a firing current usually generated from a low-voltage source such as a battery or charged capacitor, it ignites a primer material which then ignites the combustible material to produce a flash of light. Naturally, the oxygen gas aids in the above ignition.
In high-voltage lamps, the use of a filament is usually excluded by the provision of a glass or ceramic bead in which are located the extending ends of the lamp's conducting wires. Primer material serves to bridge the portions of these ends which project through the bead. High-voltage lamps also include the aforedescribed filamentary material and combustion-supporting gas. Flashing is accomplished by a firing pulse approaching a few thousand volts and provided by a piezoelectric element. In another type of high-voltage lamp, the primer is located within an indentation in the bottom of the lamp and the conductive wires extend therein.
Understandably, it is highly desirous to prevent shred interference with the lamp's ignition in both of the above types of lamps. This can occur primarily in one of two ways: either by the shreds contacting and shorting the exposed portions of the lead wires within the envelope or by the shreds contacting and lying across the primer material surface.
In both cases, the ignition voltage characteristics are altered, which in some instances can even prevent the lamp from firing. Shred interference can also reduce the firing voltage to the point that ignition is possible electrostatically. In situations wherein the lamp is used in circuitry containing several other lamps (e.g. sequential or random flash embodiments), an altered ignition voltage substantially reduces the lamp's compatibility to the desired circuit.
Various techniques for preventing shred shorting across a pair of exposed lead wires in a photoflash lamp are illustrated in U.S. Pat. Nos. 3,884,615, 3,930,784, and 4,082,494. In 3,884,615, a glass sleeve surrounds one of the lead wires and acts as an insulator therefor. A problem with this technique is that it does not readily lend itself to mass production due to the necessity for precisioned location of the sleeve with respect to the lamp's glass bead component. A problem inherent in the technique disclosed in the remaining patents cited above is the possibility of displacement of the insulative materials during rough handling, shipping, etc. of the lamp. This is particularly true with the lamp described in U.S. Pat. No. 3,930,784 wherein the small glass beads can become intermixed with the filamentary combustible material, especially during handling wherein the lamp is inverted. Another disadvantage of the lamp of U.S. Pat. No. 3,930,784 is that such relatively large quantities of beads as required occupy portions of the lamp normally reserved for the essential, combustion-supporting atmosphere. The potentially adverse results of such a requirement are self-explanatory.
All of the above patents also fail to recognize the problems caused by shred interaction with the surface of the desired primer material. One method of attempting to solve this is shown in U.S. Pat. No. 3,602,619, wherein a hollow glass tube surrounds the mass of primer material and extends thereabove. The portions of the lead wires which were exposed in the earlier mentioned patents are embedded within the lamp envelope's seal (or bottom) portion. A problem inherent in U.S. Pat. No. 3,602,619 is that the lamp's filamentary shreds can still settle within the open tube as a result of rough handling of the lamp. Still further, the lamp does not lend itself to known techniques of mass production due to the extreme difficulty of positioning the glass tube at the location required.
It is believed, therefore, that a photoflash lamp which is capable of facilely preventing shred interference between the lamp's combustible filaments and both the lamp's primer material and any portion of the lamp's conductive wires which are exposed within the envelope would constitute an advancement in the art.
It is also believed that a method of making a lamp having the above unique capability would constitute an art advancement.